1,2,4-triazole is mainly used in the production of plant protection agents and by the pharmaceutical industry.
For the preparation of 1,2,4-triazole many processes are known. Of these processes those are now disclosed which are closest to the present invention.
According to the Luxemburgian patent specification No. 61,617 1,2,4-triazole can be prepared by reacting 1 mole of hydrazine and 3 moles of formamide at a temperature of 90.degree. to 260.degree. C. in accordance with equations 1 and 2. ##STR1##
The main disadvantage of this process is the high demand on formamide. At the same time a great part of the ammonia contents of formamide gets lost as waste and therefore the industrial realization of this process is uneconomical.
The German patent specification No. 2,802,491 discloses also a process starting from these two reagents and further from ammonia. According to this process the reaction is carried out at a temperature of 100.degree. to 250.degree. C., preferably at 110.degree. to 220.degree. C., in an apparatus comprising 3 or 4 reactors in series while the gases and vapours are condensed at different temperatures and the condensates as well as the gases and vapours are recycled into one or another reactor. In this process instead of 3 moles of formamide (3-n) moles of formamide are used where 0.3.ltoreq.n.ltoreq.1, that is, the formamide is partly substituted by ammonia--c.f. equation 3. EQU H.sub.2 N--NH.sub.2 +(3-n)H--CO--NH.sub.2 +nNH.sub.3 .fwdarw.(II)+2H.sub.2 O++2NH.sub.3 +(1-n)CO (3) EQU 0.3.ltoreq.n.ltoreq.1
This process is very complicated in view of the necessity of ensuring the balance of the cascade system, further of the cooling of the gaseous and vaporous products to different temperatures and the distribution of the condensates as well as of the gases, at the same time the reduction of the consumption of formamide is not significant.
The triazole ring can also be formed via diformylhydrazine (C. Ainsworth and R. B. Jones: J. Am. Chem. Soc. 1955. 77, p. 621-24). Diformylhydrazine was prepared from formic acid and hydrazine according to equation 4 by heating for 12 hours at a temperature of 100.degree. C. with a yield of altogether 60%. EQU H.sub.2 N--NH.sub.2 +2H--COOH.fwdarw.(I)+2H.sub.2 O (4)
Diformylhydrazine can be also obtained from hydrazine and formamide at a temperature of 100.degree. C. within 2 hours; the yield is, however, only 80% (c.f. equation 1). The ring closure of diformylhydrazine to 1,2,4-triazole can be carried out with ammonia according to equation 5, namely with condensed ammonia, by heating the reaction mixture under pressure at a temperature of 200.degree. C. for 24 hours. EQU (I)+NH.sub.3 (II)+2H.sub.2 O (5)
1,2,4-Triazole is formed with a yield of 70 to 80%. The total yield, based on hydrazine, is in both cases less than 60%. These processes are difficult and uneconomical.
Thus, for the ring closure of diformylhydrazine formamide, ammonia or formamide and ammonia, respectively, are used (c.f. equations 2 and 3). Besides the main reaction, however, numerous side reactions can take place, e.g. the reactions represented by equations 6, 7 and 8, see on the next page [A. Etienne: Traite de chimie organique (V. Grignara et al. editor) 21, 898, Masson, Paris 1953; A. Hetzheim and K. Mockel: Advan.Heterocyclic Chem. 7, 183-224 (1966); G. H. Schwab: Z.anorg. allg. Chem. 262, 41-8 (1950)].